Several processes for producing cyanobenzyl compounds are already known.
1. Cyanobenzyl alcohol compounds
Exemplary processes for producing p-cyanobenzyl alcohol, a typical cyanobenzyl alcohol compound, are as follows.
p-Cyanobenzyl alcohol is synthesized through reduction of a p-cyanobenzoic acid ester or p-cyanobenzaldehyde using a reducing agent formed of a hydride compound such as sodium borohydride (Kikugawa, Y., Chem. Pharm. Bull, 24 (1976) 1059; and Hilborn, J. W., et al., J. Am. Chem. Soc., 116 (1994) 3337). Alternatively, p-cyanobenzaldehyde is reduced through water gas shift reaction in the presence of a rhodium cluster-on-polymer catalyst (Kaneda, K., et al., Tetrahedron Letters, 38 (1997) 3005).
2. Cyanobenzyl halide compounds
An exemplary process for producing p-cyanobenzyl chloride, a typical cyanobenzyl halide compound, is as follows.
p-Cyanobenzyl chloride is synthesized through mono-chlorination of p-tolunitrile (J. Am. Chem. Soc., 65 (1943) 2282: L. Blicke).
3. Cyanobenzyl acyloxy compounds
Exemplary processes for producing p-cyanobenzyl acetate, a typical cyanobenzyl acyloxy compound, are as follows.
p-Cyanobenzyl acetate is synthesized through reaction of p-cyanobenzyl chloride and sodium acetate in an alcohol solvent (Banse, Chem. Ber., 27 p2171 (1894)). Alternatively, p-cyanobenzyl acetate is synthesized through acetylation of p-cyanobenzyl alcohol (A. L. Baumstark, et al., Tetrahedron Letters, 25 p169 (1984)).
The above processes for producing p-cyanobenzyl compounds have disadvantages as described below.
1. p-Cyanobenzyl alcohol
When reduction is carried out by use of a reducing agent formed of a hydride, such an expensive reagent is required in an amount greater than the stoichiometric amount, to thereby produce a large amount of waste. When reduction is carried out using hydrogen, an expensive rhodium catalyst is employed. Thus, both processes are economically disadvantageous.
2. p-Cyanobenzyl chloride
Hazardous chlorine gas is used for chlorinating p-tolunitrile, and selectivity of monochlorination is insufficient.
3. p-Cyanobenzyl acetate
p-Cyanobenzyl chloride or p-cyanobenzyl alcohol serving as a raw material is not easily available as a general-purpose raw material.
As described above, the synthesis of p-cyanobenzyl compounds by use of a conventionally known technique is cumbersome, and production of high-purity compounds is difficult. In addition, raw materials such as a p-cyanobenzoic acid ester, p-cyanobenzaldehyde, and p-tolunitrile are not easily available. Thus, the above processes are unsatisfactory for production of cyanobenzyl compounds at high yield and high purity on an industrial scale.
In view of the foregoing, the present invention is directed to provision of an industrially advantageous process for producing cyanobenzyl compounds under mild conditions from relatively easily available cyanobenzylamine having a cyano group on the benzene ring or a compound thereof which is ring-substituted with a chlorine atom, a fluorine atom, etc. (hereinafter these compounds may generally be referred to as "cyanobenzylamine compounds").